The invention relates to a high voltage generator comprising a first series of voltage multiplying stages, each stage comprising a diode and a capacitor one terminal of which being connected to the cathode of the respective diode, wherein every cathode of a diode is connected to the anode of the diode of the next voltage multiplying stage, a clock generator which is able to generate clock pulses being 180.degree. out of phase with one another and being supplied alternately to the other terminal of the capacitors of successive voltage multiplying stages, the last diode in the series having a high voltage output and said high voltage output being connected to feed-back means, which modifies said two clock pulses in dependence on the voltage on the high voltage output.